In the U.S, former United States Surgeon General Koop and some others have claimed that condoms are ineffective against HIV transmission during anal sex, holding that condoms are somewhat permeable to the tiny HIV virus. These claims have been disputed by medical researchers, who generally view correctly used condoms as effective protection. Some studies have shown that, even with the best of intentions, determined condom users sometimes forget to put them on before sex, so that the transmission rate remains disturbingly high. Advocates of safe sex education point out that it has to start at an early age to be effective, a notion which arouses even heavier opposition from conservatives given the taboo of child sexuality.